If someone starts krias shma assuming he will finish in time to finish and hear the chazzan repeat Hashem Elokeichem Emes. but the chazzan says it before he finishes shma what should he do?
A person who is in middle of saying shema, and hears the chazzan saying the words Hashem Elokeichem Emes, should stop saying shems and listen to the words of the chazzan. After that he will continue saying shema.
Sharei teshuva O:CH 61-2, Oz Nidberu 4-41.